Different families and species (chickens are domesticated Red Junglefowl, in Phasianidae & Guineafowl are domesticated Helmeted Guineafowl in Numididae). Free-range Guineafowl will often roost indoors if they are comfortable in the area, or will use trees. They fly very well and will roam quite far from their home. The wild versions will lay up to 30 eggs per clutch, so I assume the domestics will lay more.
Guineas need more than two to thrive. They seem to need about 4 to make what is called the "unimind". THey Continually talk to each other and can alert to just about any thing. This is why you need more than 2 because they will alert to just about anything.
They fly very remarkably. I have seen my Guineas fly well above the chicken barn and over to another building 100 feet away and land on this roof. So you will not be able to keep them fenced in.
They do go to the chicken bard at night, but I trained them and have had them from day olds.